This invention relates, in general, to gas turbines; and, in particular to catalytic reactors for accelerating carbon monoxide and hydrocarbon oxidation reactions during the combustion process. More specifically, this invention relates to a reactor support apparatus which is generally positioned between the combustion chamber and the transition zone of a gas turbine.
Concurrent with demands for more electrical power, increased public pressures for good air quality have resulted in stringent requirements regulating allowable gas turbine emissions. Such regulations necessitate recourse to both clean burning fuels and advanced gas turbine combustion systems that produce less objectionable emissions during burning. One preferred method of reducing objectionable emissions is through the use of direct catalytic combustion of the fuel within the gas turbine combustor. Direct catalytic combustion requires the use of a catalytic reactor in the combustion gas stream to achieve low levels of carbon monoxide and unburned hydrocarbons simultaneously with reduced oxides of nitrogen. The catalytic reactors are usually comprised of ceramic or metal substrates which are coated with catalyst materials such as noble metals. The catalytic reactors may be described as cylinders having a cross section which is geometrically shaped such as honeycombed. It is well known that these catalytic reactors operate in an environment of elevated temperatures and consequent thermal changes. Also by nature of a rotating machine environment shock and vibratory loadings sometimes occur. In addition, in the high pressure environment of a combustion chamber it is important that leakage of combustion products out of the combustion path does not occur. It is also well known that ceramic materials are brittle thereby requiring extra attention to the foregoing environment. All in all, it can be concluded that special attention must be given to the support structure for a catalytic reactor if it is to be successfully implemented into a gas turbine for the successful reduction of NOx emissions.
One such specially devised mounting structure for a catalytic reactor is found in U.S. Pat. No. 4,432,207 issued to inventors Davis and Steber, and assigned to the assignee of the present invention. In that patent, a tubular heat shield was interposed between the outer circumference of the reactor bed and the support cylinder in order to permit admission of an adequate amount of purge air: i.e., air which prevents the ingress of combustion products into the space between the reactor and the support cylinder. At the same time, the heat shield prevents overcooling of the reactor by blocking direct impingement cooling of the reactor surface. It should be carefully noted that shock loadings upon the reactor are mitigated through the use of axial support springs which serve to center the reactor within the support structure. The foregoing is exemplary of the state of the art prior to the present invention.
It is an object of the present invention to improve upon the state of the art by providing a catalytic reactor support structure which is less complex than previous known structures.
It is another object of the invention to admit an adequate amount of purge air to prevent the ingress of unburned fuel or products of combustion into the space between the reactor and the support cylinder.
It is another object of the present invention to provide a thermal barrier between the catalytic reactor and the support cylinder without resort to a metal tubular shield.
It is another object of the present invention to protect the reactor against shock loadings by means of an air cushion which surrounds the catalytic reactor.
It is yet another object of the present invention to provide a support for a catalytic reactor which will automatically recenter the catalytic reactor if it is displaced in the radial direction.
The novel features believed characteristic of the present invention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof may best be understood with reference to the following description taken in connection with the accompanying drawings.